The invention relates to a protective layer and/or planarization layer for a self-assembling monolayer (SAM), as used in particular in circuit board fabrication, in the functionalization of copper blanks, as for example in the production of passive components such as capacitors and resistors.
The density of integration in circuit board fabrication goes up with increasing miniaturization, hence giving rise to the need for components, especially passive components such as resistors and capacitors, to be integrated directly into the circuit board. The space saving on transition to 3D population has a positive effect in turn on the costs situation.
Rising cycle frequencies in commodity products, such as computer main boards or cell phone circuit boards, in conjunction with data buses that are becoming ever broader, mean that there is an increased requirement for capacitive sinks in order to ensure reliable communication between the components (signal-to-noise ratio). While the ratio between capacitors and resistors was formerly at a level of 1:1, it has now risen to 3:1.
In order to increase the mechanical stability of the SAMs, which almost exclusively determine the leakage current characteristics of the components, such as the capacitors, for example, DE 10 2008 048 446 applies to the self-assembling monolayer, for the purpose of stabilization and/or for the local planarization of the capacitor or component, a supporting polymer, in other words a thin polymer layer. This layer is referred to below as a protective layer. Typically, with the known protective layers, an integration density of 50 pF/mm2 is produced with a dielectric constant of 3.17 for an effective polymer layer thickness of approximately 550-600 nm, whereas for an integration density of 150 pF/mm2 an effective layer thickness is 180-200 nm. A greater amount of polymer is introduced into the sinks, while the peaks carry a thinner polymer film (see FIG. 1).
For planarization, use has to date been made of any desired polymers as support polymers, provided they are compatible with the circuit board processes.
A disadvantage of the related art is the low dielectric constant of the protective layer, which in turn determines the integration density, which, as described above, ought to be increased for the purpose of miniaturization and for providing a broad capacitance spectrum.